The present invention relates to a process for preparing a fluorine-containing elastomer having a reduced metal content, and further relates to the fluorine-containing elastomer obtained by the process, a composition containing the fluorine-containing elastomer and a molded article obtained from the composition.
Fluorine-containing resins (plastics) have been used in a large amount for important parts such as chemical pipe, square tank and basket for silicon wafer which have a direct influence on semiconductor products in the semiconductor production process where strict requirements for cleanliness are demanded. Therefore reduction of contents of metal components, TOC (total organic carbon) and particle impurity in the fluorine-containing resins has been attempted positively.
Also with respect to fluorine-containing elastomers comprising mainly a vinylidene fluoride (VdF) unit or tetrafluoroethylene (TFE) unit, as they are called fluorine-containing rubbers, they are used in the field of rubber and treatments employed in that field are applied thereto. Thus handling thereof including vulcanization treatment differs largely from that in the field of fluorine-containing resin. Actually when the elastomer is used for a composition for vulcanization, since a filler, vulcanizing agent, vulcanization accelerator, acid acceptor, etc. are added thereto and since a major application of a rubber material is a sealing material and a contact portion thereof with chemicals is limited to a very small area unlike the chemical pipe, square tank and basket, there have been almost no problem particularly with purity of the fluorine-containing elastomer and presence of impurities.
On the other hand, an attention has been attracted recently to the fluorine-containing elastomer as a sealing material for semiconductor production apparatuses which is used under critical environment in the field of production of semiconductors from the viewpoint of excellent chemical resistance, solvent resistance and heat resistance thereof.
However in the field of production of semiconductors, reduction of cost of semiconductor chips has been advanced rapidly because of high integration and enhancement of yield, and as a result, a sealing material used on semiconductor production apparatuses is strongly required not to contain metal components, TOC and particles and not to release them in the semiconductor production apparatuses (so-called xe2x80x9ccleaningxe2x80x9d of a sealing material). Therefore it is not enough to employ only a conventional method of washing the sealing material with various solvents.
For example, JP-B-59-46985 discloses a sealing material produced by molding a composition containing a fluorine-containing elastomer by using a peroxide as a vulcanizing agent without adding a metal compound as an acid acceptor, and JP-A-9-500163 discloses a sealing material produced by molding a composition prepared by using an organic acid acceptor without using a metal oxide as an inorganic acid acceptor. However only by those approaches for cleaning during vulcanization, a metal content in the fluorine-containing elastomer used for those sealing materials cannot be reduced sufficiently. Also it has become necessary to take measures against metal ingredients contained in the fluorine-containing elastomer because the sealing materials are used in a plasma atmosphere causing a reduction of weight or in an environment where an abrasion of the sealing material represented by a gate valve arises due to open-close operations.
Further according to a technique described in JP-A-9-500163, O-ring having a reduced metal content is intended to be obtained by extracting a metal component through a specific method after it is produced by molding a composition containing a fluorine-containing elastomer through usual method. However even if such an extra step is employed, since the fluorine-containing elastomer itself is prepared through a conventional method, the content of metal component: being present therein is absolutely much and as a result, cannot be reduced sufficiently.
On the other hand, JP-A-8-506604 describes a technique for vulcanizing by irradiating electron beams without using a metal compound. However the vulcanized product still contains a metal component which seems to be attributable to a coagulating agent, in an order of 100 ppm.
Namely a conventional fluorine-containing elastomer may contain metal components substantially because metal compounds such as a polymerization initiator and coagulating agent are used for preparation thereof. Also since metal compounds such as a vulcanizing agent, vulcanizing accelerator, acid acceptor and filler are used for producing a sealing material from such a fluorine-containing elastomer, the sealing material contains metal components and further particles are present on its surface.
Also conventional evaluation of content of metal components is made with an amount of elution under a specific elution (extraction) conditions, and therefore a present situation is such that under different treating conditions, an amount of elution also differs remarkably.
Such being the case, a fluorine-containing elastomer being capable of complying with every environment and treatment and having substantially reduced metal components therein and a sealing material produced from the fluorine-containing elastomer and having a sufficiently reduced content of metal components have not yet been obtained.
In view of the above-mentioned fact, an object of the present invention is to provide a method of substantially reducing a content of metal components inside of the fluorine-containing elastomer in the preparation thereof, and further as a result, to provide a molded article, particularly a sealing material produced from the fluorine-containing elastomer having a sufficiently reduced content of metal components.
The present invention relates to the method of reducing a metal content of a fluorine-containing elastomer through preparation thereof, in which a metal compound is not blended during emulsion-polymerization of a fluorine-containing monomer.
Further the present invention relates to the method of reducing a metal content of a fluorine-containing elastomer through preparation thereof without using a metal compound, in which among materials excluding a gaseous monomer which are used for polymerization of a fluorine-containing monomer, coagulation and drying, at least one material contains substantially no metal component.
In that case, it is preferable that the material used for polymerization of a fluorine-containing monomer, coagulation and drying is water for a polymerization medium.
Also it is preferable that the material used for polymerization of a fluorine-containing monomer, coagulation and drying is a coagulating agent for coagulation.
Further it is preferable that the material used for polymerization of a fluorine-containing monomer, coagulation and drying is a non-water-soluble solvent which has compatibility with the fluorine-containing elastomer containing water and is added when separating water from the coagulated fluorine-containing elastomer containing water.
Further the present invention relates to the method of reducing a metal content of a fluorine-containing elastomer through preparation thereof, in which emulsion-polymerization of the fluorine-containing elastomer is carried out while maintaining an emulsion in a weak alkaline state.
Further the present invention relates to the method of reducing a metal content of a fluorine-containing elastomer through preparation thereof, in which coagulation is carried out after an emulsified dispersion of the fluorine-containing elastomer is filtrated to remove contaminants.
Further the present invention relates to the method of reducing a metal content of a fluorine-containing elastomer through preparation thereof, in which coagulation of an emulsified dispersion of the fluorine-containing elastomer is carried out by using an acid containing no metal element.
Further the present invention relates to the method of reducing a metal content of a fluorine-containing elastomer through preparation thereof, in which to the fluorine-containing elastomer containing water obtained by coagulation of an emulsified dispersion of the fluorine-containing elastomer is added a non-water-soluble solvent having compatibility with the fluorine-containing elastomer containing water to separate the water therefrom.
Further the present invention relates to the method of reducing a metal content of a fluorine-containing elastomer through preparation thereof, in which a clean gas is used for drying a fluorine-containing elastomer containing water obtained by coagulation of an emulsified dispersion of the fluorine-containing elastomer or, a coagulated elastomer obtained by adding, to the fluorine-containing elastomer containing water, a non-water-soluble solvent having compatibility therewith to separate the water therefrom.
Further the present invention relates to the method of reducing a metal content of a fluorine-containing elastomer through preparation thereof, in which a vessel laminated with a fluorine-containing resin film or polyethylene film on its part coming into contact with the coagulated elastomer, a vessel made of a fluorine-containing resin or a vessel made of polyethylene resin is used.
Further the present invention relates to the method of reducing a metal content of a fluorine-containing elastomer which comprises at least two of the above-mentioned methods.
Further the present invention relates to the method of reducing a metal content of a fluorine-containing elastomer through preparation thereof without using a metal compound, in which the elastomer is prepared by using materials containing substantially no metal component as all the materials used for polymerization of a fluorine-containing monomer, coagulation and drying, by employing an equipment, a part of which comes into contact with an emulsion, emulsified dispersion or coagulated fluorine-containing elastomer containing water and is made of or lined with a fluorine-containing resin or polyethylene resin, and by drying with a clean gas.
The present invention relates to the fluorine-containing elastomer having a metal content of not more than 50 ppm, preferably not more than 10 ppm, more preferably not more than 1 ppm.
Also the present invention relates to the fluorine-containing elastomer having a metal content of not more than 50 ppm, preferably not more than 10 ppm, which is obtained by one of the above-mentioned methods or by a combination of two or more thereof.
In that case it is preferable that the fluorine-containing elastomer comprises 40 to 90% by mole of tetrafluoroethylene, 10 to 60% by mole of perfluorovinylether represented by the formula (1):
CF2xe2x95x90CFxe2x80x94ORf
wherein Rf is a perfluoroalkyl group having 1 to 5 carbon atoms or a perfluoroalkyl(poly)ether group having 3 to 12 carbon atoms and 1 to 3 oxygen atoms, and 0 to 5% by mole of monomer giving a curing site.
Also it is preferable that the above-mentioned fluorine-containing elastomer comprises 30 to 85% by mole of vinylidene fluoride, 15 to 40% by mole of hexafluoropropylene and 0 to 30% by mole of tetrafluoroethylene.
Also it is preferable that the above-mentioned fluorine-containing elastomer comprises 10 to 90% by mole of vinylidene fluoride, 10 to 40% by mole of perfluorovinylether represented by the formula (1): CF2xe2x95x90CFxe2x80x94ORf, wherein Rf is as defined above, and 0 to 80% by mole of tetrafluoroethylene.
Also it is preferable that the above-mentioned fluorine-containing elastomer comprises 40 to 90% by mole of vinylidene fluoride, 3 to 35% by mole of perfluoro(methyl vinyl ether) (PMVE), 0 to 25% by mole of hexafluoropropylene, 0 to 40% by mole of tetrafluoroethylene, and 0.005 to 1.5% by mole of iodine-containing monomer (IM) as the monomer giving a curing site (cf. WO96/17877). As the iodine-containing monomer, iodine-containing fluorinated vinyl ethers represented by the formula (4): I(CH2CF2CF2O)m[CF(CF3)CF2O]nCFxe2x95x90CF2, wherein m is an integer of 1 to 5, n is 0 or an integer of 1 to 3, can be used preferably.
Also it is preferable that the above-mentioned fluorine-containing elastomer is a fluorine-containing multi-segment polymer having an elastomeric fluorine-containing polymer chain segment and a non-elastomeric fluorine-containing polymer chain segment; the elastomeric fluorine-containing polymer chain segment comprises 40 to 90% by mole of tetrafluoroethylene, 10 to 60% by mole of perfluorovinylether represented by the formula (1):
xe2x80x83CF2xe2x95x90CFxe2x80x94ORf
wherein Rf is as defined above, and 0 to 5% by mole of monomer giving a curing site, and the non-elastomeric fluorine-containing polymer chain segment comprises 85 to 100% by mole of tetrafluoroethylene and 0 to 15% by mole of the formula (2):
CF2xe2x95x90CFxe2x80x94Rf1
wherein Rf1 is CF3 or ORf2, in which Rf2 is a perfluoroalkyl group having 1 to 5 carbon atoms.
Also it is preferable that each of the above-mentioned fluorine-containing elastomers contains a polymer chain having iodine and/or bromine at its end and/or side chain.
Also it is preferable that the above-mentioned fluorine-containing elastomers have nitrile group.
Further the present invention relates to the composition containing the above-mentioned fluorine-containing elastomer.
Further the present invention relates to the molded article obtained from the above-mentioned composition.
The present invention also relates to the molded article having a metal content of not more than 50 ppm, preferably not more than 10 ppm.
It is preferable that the above-mentioned molded article is a sealing material for semiconductor production apparatuses.
Further the present invention relates to the method of reducing a metal content of the fluorine-containing polymer through preparation thereof, in which equipment lined with a fluorine-containing resin on its portion coming into contact with materials for polymerization and a produced polymer is used.
In that case, it is preferable that the equipment lined with a fluorine-containing resin is a polymerizing equipment such as a polymerization vessel and agitation blades and baffle plates thereof, coagulation equipment, washing equipment, drying equipment or pipes thereof.
Also it is preferable that the fluorine-containing resin is tetrafluoroethylene/perfluoro(alkyl vinyl ether) copolymer (PFA).